There are places you're not going to want to miss when in the Island Park area. First, there's the aforementioned Mount Two Top, where you can see into three states-Montana, Idaho and Wyoming. There's also Big Springs, where you can feed the trout or catch a glimpse of a moose or other wildlife that frequent the headwaters of the Henry's Fork River. Or head to Mesa Falls, where you'll stand right at the edge of the river as it cascades over an 85-foot drop. You can ride to Cave Falls (east out of Ashton) inside Yellowstone National Park or head to Warm River Springs and see the river come out of the mountain.
Because Island Park is on the west side of the mountain dividing Idaho from Montana, it manages to get several more inches (up to 75 more) of snow than does West Yellowstone, thanks to the fact that the storm clouds get hung up on the mountains before slipping over into West Yellowstone.
Parking lots can be found at various places along Highway 20, as can most of the eating and sleeping establishments. Island Park can get crowded on the weekends as sledders from all sorts of cities head to the hills, but hit the area during the week and you'll see fewer crowds.